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RÉVISION DES CARTES 
CARTOGRAPHIC UTILITY OF SPACE PHOTOGRAPHS 
Frederick J. DOYLE 
U.S. Geological Survey 
In October 1971, an International Symposium on Orthophotomapping was held in Paris, 
France. At that time the theoretical basis for preparing orthophotomaps from space photography 
was presented [1] . Also presented were the characteristics of the imaging systems to be carried 
on the Earth Resources Technology Satellite (ERTS-1) and the Skylab . This was followed by a 
projection of the cartographic applications which could be accomplished from these records. 
The ERTS-1 spacecraft was launched in July 1972, and has been operating continuously 
since that time. The three manned occupations of Skylab have been completed and all data has 
been obtained. Though it is still too early to reach final conclusions on the value of these records, 
it is appropriate to review what has been accomplished, and what has been learned about the uti- 
lity of these types of space photographs for cartographic applications. 
Theoretical Basis 
The major advantages of space photography for preparation of orthophotomaps are : 
1.- Narrow angular field. This reduces image displacements due to topographic relief, and makes 
possible the production of orthophoto products without the necessity of differential rectification. 
2.- High image resolution. This is made possible by the combination of narrow field optical sys- 
tems and extremely stable vibration-free platforms. 
3.- Synoptic view. The ultra-high altitude of space vehicles makes possible a wide area of coverage 
per frame despite the narrow angular field. 
Counteracting these advantages are : small image scale. Despite relatively long focal 
lengths, the extreme altitude produces small scale images. 
In the 1971 paper it was suggested that space photographs could be enlarged until their 
equivalent resolution was about 10 line pairs per millimeter (1p/mm). 
R 
EE 
MTs 
M = recommended magnification from original photograph to photo ima ge map product 
B, = resolution of original record (lp/mm). 
This criterion also imposed a relationship between the ground resolution which could be portrayed 
and the scale of the photo image map product. 
R_ = 107415 
g m 
R, = ground resolution (meters) Sn published map scale number 
As willbe seen shortly, these values proved conservative, and useful products can be made based 
on the criterion of 5 lp/mm rather than 10. This permits greater magnification between original 
photography and published map, and permits lower ground resolution on the final map. 
A relationship was also derived to express the maximum terrain relief which could be 
accommodated in a single frame of imagery without exceeding National Map Accuracy Standards 
(NMAS) for planimetric accuracy in the published orthophoto product. 
  
5H h = allowable terrain relief (meters) 
BERT H = spacecraft altitude (meters) 
p r = maximum radial distance from nadir point of original image (mm) 
2T.